1. Field of the Invention
Embodiments of the invention relate to a thin film transistor array substrate having excellent characteristics through a reduction in an off-current and a method for manufacturing the same.
2. Discussion of the Related Art
The importance of flat panel displays is recently increasing with the growth of multimedia. Thus, various types of flat panel displays such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and organic light emitting diode (OLED) displays have been put to practical use.
Out of the flat panel displays, the liquid crystal display has visibility, which is better than a cathode ray tube (CRT), and average power consumption and an amount of light generated, which are less than the cathode ray tube (CRT). Further, because the OLED display has a fast response time of 1 ms or less, low power consumption, and a self-emitting structure, there is no problem in a viewing angle of the OLED display. Thus, the OLED display has been considered as a next generation display.
An active matrix liquid crystal display using thin film transistors is driven by a voltage held by capacitances of the thin film transistors, which are connected to pixel electrodes. In addition to basic characteristics of the thin film transistor including a mobility, a leakage current, etc., durability and electrical reliability capable of maintaining long lifespan are very important in the thin film transistor of the active matrix liquid crystal display.
The thin film transistor includes a gate electrode, an active layer, a source electrode, and a drain electrode. The active layer is formed of amorphous silicon or polycrystalline silicon. Amorphous silicon mainly used to form the active layer has the advantage of a simple formation process. Hence, the manufacturing cost of the active layer may be reduced. However, a behavior of electrons and a behavior of holes are not free because of characteristic of amorphous silicon, in which the Fermi level exists in the middle of an energy gap. Hence, a leakage current resulting from a hole current increases in an off-region. As a result, a crosstalk is generated in an image, and a reduction in the image quality, for example, a spot is generated.